Physicians and health experts generally agree that a diet low in saturated fats and cholesterol can reduce the likelihood of heart and circulatory diseases. Consumer awareness of the health benefits associated with maintaining a diet low in fat and cholesterol has increased, along with the demand for food products low in these components. Because of its low fat content, skim milk currently has large applications in such low fat food products.
Whole milk is a dilute emulsion combined with a colloidal dispersion in which the continuous phase is a solution. Whole milk has a fat content typically between about 3.3% to about 3.4%, and about 14 mg of cholesterol per 100 g milk.
In milk products, the majority of the fat, and about 80% to about 85% of the total cholesterol is present in the cream. The cream is predominantly milk fat globules. In the milk fat, the cholesterol is thought to be distributed between the milk fat globule membrane and the bulk lipid. It was once believed that when the membrane was separated from the milk fat globules and the butter oil was isolated from the milk fat globules, that about 90 percent or greater of the cholesterol was equilibrated in the butter oil and about 5 percent or greater was in the membrane. Thus, it was believed that there was a high correlation between fat content and the amount of cholesterol in milk. However, it is now believed that there is very little connection between cholesterol content and fat content. The cream is rich in cholesterol: 100 g of cream with a fat content of 36% contains approximately 125 mg of cholesterol. The USDA National Nutrient Database for Standard Reference lists whipping cream (100 g) with a 37% fat content as containing 137 mg cholesterol.
Skim milk is typically obtained by centrifugation of whole milk to separate the cream from the continuous phase, or skim milk. Upon centrifuging, the cream, an oil rich phase, separates and floats on top of the skim milk. The skim milk thus obtained, contains about 2 mg of cholesterol per 100 g of skim milk, less than about 0.5% fat, and about 10% solids. Thus, the skim milk contains about 10% to about 20% of the total cholesterol content of whole milk.
The cholesterol in milk products is thought to be associated with triglycerides, milk fat globules and complex proteins. Cholesterol in skim milk is thought to exist in three forms as being complexes with:                (i) residual triglyceride droplets not removed in the skimming process;        (ii) lipoprotein particles sloughed off from milk fat globule membranes in the skimming process; and        (iii) proteins contained in the serum albumin.When skim milk, reduced-fat, or whole milk is concentrated, its cholesterol content increases proportionally. For example, nonfat dry milk has a cholesterol content of about 20-30 mg per 100 grams. Therefore, the use of skim milk, reduced-fat or whole milk as an ingredient in low fat foods can contribute significant amounts of cholesterol to these foods.        
Several approaches have been utilized for removing the cholesterol from milk fats. For instance, methods of removing cholesterol from fats by contacting with adsorbent materials such as silica gel and activated carbon. When applied to milk products, such adsorbents have been found to either be too impractical for commercial use or to lack specificity for cholesterol adsorption. Supercritical extraction processes have also been used; however, such processes involves extreme process conditions and is generally too expensive for large commercial applications. Also, the use of oils as extractants of cholesterol from milk have also been used. However, the use of such non-dairy additives does not allow for the dairy products to be sold as an unadulterated product.